Laser devices using a semipolar plane

ABSTRACT

An optical device includes a gallium and nitrogen containing substrate comprising a surface region configured in a (20-2-1) orientation, a (30-3-1) orientation, or a (30-31) orientation, within +/−10 degrees toward c-plane and/or a-plane from the orientation. Optical devices having quantum well regions overly the surface region are also disclosed.

This application is a continuation of U.S. application Ser. No.16/118,217, filed Aug. 30, 2018; which is a continuation of U.S.application Ser. No. 15/424,551, filed Feb. 3, 2017; which is acontinuation of U.S. application Ser. No. 14/883,137, filed Oct. 14,2015; which is a continuation of U.S. application Ser. No. 14/604,223,filed Jan. 23, 2015, now U.S. Pat. No. 9,166,374, issued Oct. 20, 2015;which is a continuation of U.S. application Ser. No. 13/651,291, filedOct. 12, 2012, now U.S. Pat. No. 8,971,370, issued Mar. 3, 2015; whichclaims the benefit of U.S. Provisional Application No. 61/546,792, filedOct. 13, 2011; each of which are incorporated by reference herein intheir entirety.

BACKGROUND

The present invention is directed to optical devices and relatedmethods. In particular, the invention provides a method and device foremitting electromagnetic radiation using nonpolar or semipolar galliumcontaining substrates such as GaN, AlN, InN, InGaN, AlGaN, and AlInGaN,and others. More particularly, the present invention provides a methodand device using a gallium and nitrogen containing substrate configuredon the {20-21} family of planes or an off-cut of the {20-21} family ofplanes toward the plus or minus c-plane and/or toward the a-planeaccording to one or more embodiments, but there can be otherconfigurations. Such family of planes include, but are not limited to,(30-3-2), (20-2-1), (30-3-1), (30-32), (20-21), (30-31) or anyorientation within +/−10 degrees toward c-plane and/or a-plane fromthese orientations. The invention can be applied to optical devices,lasers, light emitting diodes, solar cells, photoelectrochemical watersplitting and hydrogen generation, photodetectors, integrated circuits,and transistors.

In the late 1800's, Thomas Edison invented the light bulb. Theconventional light bulb, commonly called the “Edison bulb,” has beenused for over one hundred years for a variety of applications includinglighting and displays. It uses a tungsten filament enclosed in a glassbulb sealed in a base, which is screwed into a socket coupled to a powersource. Unfortunately the Edison light bulb dissipates most of the powerconsumed as thermal energy. It routinely fails due to thermal expansionand contraction of the filament element. Furthermore light bulbs emitlight over a broad spectrum, much of which does not result in brightillumination or due to the spectral sensitivity of the human eye.

In 1960, the laser was first demonstrated by Theodore H. Maiman atHughes Research Laboratories in Malibu. This laser utilized asolid-state flash lamp-pumped synthetic ruby crystal to produce redlaser light at 694 nm. By 1964, blue and green laser output wasdemonstrated by William Bridges at Hughes Aircraft utilizing a gas laserdesign called an Argon ion laser. The Ar-ion laser utilized a noble gasas the active medium and produce laser light output in the UV, blue, andgreen wavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ionlaser had the benefit of producing highly directional and focusablelight with a narrow spectral output, but the wall plug efficiency was<0.1%, and the size, weight, and cost of the lasers were undesirable aswell.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green and bluelasers. As a result, lamp pumped solid state lasers were developed inthe infrared, and the output wavelength was converted to the visibleusing specialty crystals with nonlinear optical properties. A green lamppumped solid state laser had 3 stages: electricity powers lamp, lampexcites gain crystal which lases at 1064 nm, 1064 nm goes into frequencyconversion crystal which converts to visible 532 nm. The resulting greenand blue lasers were called “lamped pumped solid state lasers withsecond harmonic generation” (LPSS with SHG) had wall plug efficiency of˜1%, and were more efficient than Ar-ion gas lasers, but were still tooinefficient, large, expensive, fragile for broad deployment outside ofspecialty scientific and medical applications. Additionally, the gaincrystal used in the solid state lasers typically had energy storageproperties which made the lasers difficult to modulate at high speedswhich limited its broader deployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal which lases at 1064 nm, 1064 nmgoes into frequency conversion crystal which converts to visible 532 nm.The DPSS laser technology extended the life and improved the wall plugefficiency of the LPSS lasers to 5-10%, and further commercializationensue into more high end specialty industrial, medical, and scientificapplications. However, the change to diode pumping increased the systemcost and required precise temperature controls, leaving the laser withsubstantial size, power consumption while not addressing the energystorage properties which made the lasers difficult to modulate at highspeeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS-SHG lasers, but the specialty diodes andcrystals required make this challenging today. Additionally, while thediode-SHG lasers have the benefit of being directly modulate-able, theysuffer from severe sensitivity to temperature which limits theirapplication.

BRIEF SUMMARY

According to the present invention, techniques related generally tooptical devices are provided. More particularly, the present inventionprovides a method and device using a gallium and nitrogen containingsubstrate configured on the {20-21} family of planes or an off-cut ofthe {20-21} family of planes toward the plus or minus c-plane and/ortoward the a-plane according to one or more embodiments, but there canbe other configurations. Such family of planes include, but are notlimited to, (30-3-2), (20-2-1), (30-3-1), (30-32), (20-21), and (30-31)or any orientation within +/−10 degrees toward c-plane and/or a-planefrom these orientations. In particular, the present invention provides amethod and device for emitting electromagnetic radiation using nonpolaror semipolar gallium containing substrates such as GaN, AlN, InN, InGaN,AlGaN, and AlInGaN, and others.

In a specific embodiment, the present invention provides a gallium andnitrogen containing optical device with a substrate comprisingconfigured in either a (30-3-2), (20-2-1), (30-3-1), (30-32), (20-21),(30-31) or any orientation within +/−10 degrees toward c-plane and/ora-plane from these orientations. The device includes a separateconfinement heterostructure (SCH) region overlying the surface regionand a first barrier region overlying the separate confinementheterostructure. The device includes a plurality of quantum well regionsoverlying the surface region and a second barrier region overlying theplurality of quantum well regions. The device includes an electronblocking region overlying the second barrier region. If desired, quantumwell regions can be provided over the surface region.

Preferably, the present invention provides for a method and resultingstructure using growth of blue and green lasers and LEDs on {20-2-1}planes and off-cuts of these planes. In a preferred embodiment, the(20-2-1) planes desirably provide for high indium incorporation onoverlying growth regions, and cause the emission of highly polarizedlight. Still preferably, the (20-2-1) planes provide resulting devicescharacterized by bright emissions and narrow FWHM inelectroluminescence. In other embodiments, the method and resultingstructure can also be applied to a (30-3-2) orientation, (20-2-1)orientation, (30-3-1) orientation, (30-32) orientation, (20-21)orientation, (30-31) orientation, or any orientation within +/−10degrees toward c-plane and/or a-plane from these orientations for bluelasers and LEDs.

As an example, we had certain (20-21), (20-2-1), (30-3-1), and nonpolarm-plane substrates. With efforts for achieving high power blue laserrequiring longer wavelength, we used these orientations. The resultsusing (20-2-1), (20-21), and (30-3-1) substrates were impressive. Forexample, in the blue region we achieved bright and narrowelectroluminescence as compared to m-plane. At about 450 nm, the FWHM isless than 20 nm on (20-2-1), between 20 nm and 25 nm for (20-21) and(30-3-1), whereas m-plane that has a FWHM of 27 nm to 33 nm. We alsoobserved very polarized emissions from (20-2-1) and (30-3-1).

In the blue and green wavelength region, we observed a strong red-shiftfrom the PL wavelength to the EL wavelength and a red-shift in ELwavelength as the current is increased on (20-2-1), which is animprovement over m-plane in the blue region and an improvement of(20-21) in the green region since these ladder planes show a strongblue-shift in the respective wavelength regimes. This red-shift likelyimplies that the claimed material quality is improved over m-plane inblue or (20-21) in the green where the strong blue-shift in-part impliesin-homogenous broadening or other imperfections in the material quality.We believe the composition of (20-2-1) is homogenous.

We expect that this material on (20-2-1) with narrow FWHM andred-shifting wavelength translates into higher gain laser diodes, whichwill allow us to further improve the wall plug efficiency in both theblue and green wavelength regimes. In the blue regime, this could beimportant for high power laser diode where we would apply a very lowreflectivity (1-7%) coating to the front facet for high slopeefficiency, but still maintain low threshold current with the highmaterial gain.

In an alternative specific embodiment, the present invention provides analternative optical device and method. In a specific embodiment, thepresent invention provides an InGaN/GaN superlattice, which is usedbeneath the MQW active region. In a preferred embodiment, the opticaldevice and method provides for an improved green emission. By applyingan InGaN/GaN superlattice beneath the green MQW on (20-2-1), the presentmethod and device provides:

-   -   1. Nearly equivalent electroluminescence brightness as (20-21);    -   2. The brightness of the material in EL scaled almost linearly        with current, which implies low current droop;    -   3. The FWHM of the EL spectrum seems to be narrower than on        (20-21);    -   4. The EL red-shifts from the PL and the EL red-shifts with        increased current. Again, since blue-shift occurred on (20-21)        we believe that the material quality, and hence the gain, will        be much better on (20-2-1); and    -   5. We believe that by using (20-2-1) in green laser diode we        will be able to increase the gain and hence increase the wall        plug efficiency to greater than about 5%, greater than about 7%,        or greater than about 10%.

In other embodiments, the present device uses an InGaN/GaN superlatticestructure below the active region to improve the material quality of theactive region causing the electroluminescence to be brighter. In aspecific embodiment the super lattice also functions as a separateconfinement heterostructure (SCH) in a laser diode. This superlattice isrequired for good epi quality, but will also help guide the optical modefor increased optical confinement within the gain-providing quantum welllayers. In a specific embodiment, the superlattice is part of thewaveguide. In a specific embodiment, the present method and device maybe configured with the following.

-   -   1. The mode made be lossy or not optimized for modal gain if too        few superlattice periods are used        -   For 3% In content 65 superlattice periods are desired        -   For 6% In content 35 superlattice periods are desired        -   The mode is confined with only 20 superlattice periods for            9% and 12% In content    -   2. The mode is pulled out of the QWs for high numbers of        superlattice periods        -   For 9% In content the optimum number of periods is about 45            periods        -   For 12% In content the optimum number of periods is about 35            periods        -   Note: The above can be configured for regular SCH and HSSCH            structures    -   3. The HSSCH gives higher gain, but the loss is lower in        superlattice structures    -   4. The optimum design will be different for 5 QW or 1 QW        structures.

The method and device here can be configured with conductive oxides, lowtemperature p-clad, n-contact scribes, beam clean-up scribes, amongothers. It can also include an indium tin oxide (ITO) or zinc oxide(ZnO) cladding region on top of a thin p-type layer such as p-GaN layeror region of 200 Å to 2000 Å for laser diodes or LEDs. Certain GaNplanes may suffer from severe thermal degradation in the active regionduring growth of the electron blocking layer and the p-cladding layerswhere elevated temperatures are used. In certain embodiments, if ZnO orITO is formed in place of a portion or substantially the p-clad layer orregion, desirable p-type material can be achieved without subjecting theresulting device to a long growth time of the p-layer.

In a specific embodiment, the method and device can also include growthof a very low temperature p-cladding on top of the quantum well or lightemitting layers. By developing epitaxial conditions that enable lowresistance p-cladding sufficient for good device performance with agrowth temperature of 700° C. to 800° C., 800° C. to 850° C., or 850° C.to 875° C. degradation to the quantum well or light emitting regions canbe reduced.

The invention enables a cost-effective optical device for laserapplications such as display technologies. The optical device can bemanufactured in a relatively simple and cost effective manner. The laserdevice uses a semipolar gallium nitride material capable of achieve agreen laser device. The laser device is capable of emitting longwavelengths such as those ranging from about 480 nm to about 540 nm, andalso from about 540 nm to about 660 nm. In alternative embodiments, thelaser device is capable of emitting blue wavelengths, e.g., thoseranging from about 420 nm to about 480 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1, 1A-2, 1B-1, and 1B-2 are diagrams of optical devicesincluding growth regions.

FIG. 2 illustrates electroluminescence output power for laser devices.

FIG. 3 illustrates electroluminescence spectral width properties forlaser devices.

FIG. 4 illustrates electroluminescence wavelength shift characteristics.

FIGS. 5 through 7 illustrate band edge adsorption data.

FIG. 8 is a diagram of a laser device.

FIG. 9 is a cross-sectional diagram of a laser device.

FIG. 10 is a refractive index diagram of a laser device.

FIG. 11 is a refractive index diagram of a super lattice structure for alaser device.

FIGS. 12A and 12B illustrates confinement factors and p-type claddingloss characteristics of laser devices.

FIG. 13 is a simplified plot illustrating effects of growth temperatureof electron blocking layer (EBL) and p-cladding layer(s) on theelectroluminescence (EL) brightness for alternative crystallographicplanes for optical devices.

FIG. 14 illustrates data for blue lasers fabricated on (20-2-1)substrates.

FIG. 15 illustrates data for a blue laser fabricated on a (30-3-1)substrate.

FIG. 16 shows an example of schematic cross-section diagram of a laserdiode with a conductive oxide layer that comprises a substantial portionof the p-type cladding region.

FIG. 17 shows another example schematic of a cross-section diagram of alaser diode with a conductive oxide layer that comprises a substantialportion of the p-type cladding region.

FIG. 18 provides an example process flow for forming a laser diode witha conductive oxide layer that comprises a substantial portion of thep-type cladding region.

FIG. 19 provides an alternative example process flow for forming a laserdiode with a conductive oxide layer that comprises a substantial portionof the p-type cladding region.

FIG. 20 is a simplified diagram of a DLP projection device according toan embodiment of the present invention.

FIG. 21 is a simplified diagram illustrating a 3-chip DLP projectionsystem according to an embodiment of the present invention.

DETAILED DESCRIPTION

FIGS. 1A-1, 1A-2, 1B-1, and 1B-2 are diagrams of optical devicesincluding growth regions according to an embodiment of the presentinvention. As shown, the laser diode is an epitaxial structureconfigured on a gallium and nitrogen containing substrate within afamily of planes, e.g., (30-3-2), (20-2-1), (30-3-1), (30-32), (20-21),(30-31) or any orientation within +/−10 degrees toward c-plane and/ora-plane from these orientations. In a specific embodiment referring toFIG. 1A-1, the gallium nitride substrate includes an n-type gallium andnitride epitaxial region, an overlying InGaN nSCH region, a lowerbarrier region, a plurality of quantum well regions, an upper barrierregion, an electron blocking region, a p-type gallium and nitrogencontaining region, and an overlying p++ GaN contact region. Referringnow to FIG. 1A-2, the gallium nitride substrate includes an n-typegallium and nitride epitaxial region, an overlying InGaN/GaNsuperlattice SCH region, a lower barrier region, a plurality of quantumwell regions, an upper barrier region, an electron blocking region, ap-type gallium and nitrogen containing region, and an overlying p++ GaNcontact region.

FIGS. 1B-1 and 1B-2 illustrate embodiments of other LED devices. Theoptical device is a laser diode epitaxial structure configured on agallium and nitrogen containing substrate within a family of planes,e.g., (30-3-2), (20-2-1), (30-3-1), (30-32), (20-21), (30-31) or anyorientation within +/−10 degrees toward c-plane and/or a-plane fromthese orientations. Referring to FIG. 1B-1 the gallium nitride substrateincludes an n-type gallium and nitride epitaxial region, a lower barrierregion, a plurality of quantum well regions, an upper barrier region, anelectron blocking region, a p-type gallium and nitrogen containingregion, and an overlying p++ GaN contact region. Referring to FIG. 1B-2,the gallium nitride substrate includes an n-type gallium and nitrideepitaxial region, an overlying InGaN/GaN superlattice region, a lowerbarrier region, a plurality of quantum well regions, an upper barrierregion, an electron blocking region, a p-type gallium and nitrogencontaining region, and an overlying p++ GaN contact region.

FIG. 2 illustrates electroluminescence (EL) output power for laserdevice structures operated in LED mode at 100 mA of injected currentaccording to embodiments of the present invention. As shown, the presentdevice gallium and nitrogen containing structure configured on the(20-2-1) plane. The plot illustrates electroluminescence output poweragainst electroluminescence wavelength at the operation current of 100mA. As shown, the present device includes laser diodes using the abovestructures made using (1) (20-2-1), (2) (m-plane), and (3) (20-21). Asshown, the laser diode structures on (20-2-1) have a certain outputpower, which is 30-75% higher than that of m-plane laser diodestructures at an emission wavelength of 450 nm to 475 nm.

FIG. 3 illustrates electroluminescence (EL) spectral width propertiesfor laser device structures operated in LED mode at 100 mA of injectedcurrent according to embodiments of the present invention. As shown, thedevice gallium and nitrogen containing structure configured on the(20-2-1) plane. The plot illustrates electroluminescence spectral width(FWHM) against electroluminescence wavelength. Shown are laser diodesusing the above structures made using (1) (20-2-1), (2) (m-plane), (3)(20-21), and (4) (30-3-1). As shown, the laser diodes configured on(20-2-1) have the narrowest FWHM than the other planes across the fullspectral width range indicating the material homogeneity will be highfor potentially better gain properties and may be a good choice for blueand green laser diodes. The narrower FWHM of (20-21) and (30-3-1) overm-plane may also indicate the potential for improved laser diodeperformance.

FIG. 4 illustrates electroluminescence (EL) wavelength shiftcharacteristics for laser device structures with injected currents of100 mA to 1A operated in LED mode according to embodiments of thepresent invention. The plot illustrates electroluminescence spectralwidth (FWHM) against electroluminescence wavelength. As shown, thepresent device includes laser diodes using the above structures madeusing (1) (20-2-1), (2) (m-plane), (3) (20-21), and (4) (30-3-1). Asshown, in the blue wavelength regime of 440-480 nm the device structuresgrown on m-plane exhibit a strong peak wavelength blueshift from 100 mAto 1A E L, which is likely due to inhomogeneous InGaN and is generallyundesirable for gain in laser diodes. Alternatively, in the bluewavelength regime of 440 nm to 480 nm the device structures grown on(20-21), (30-3-1) and (20-2-1) exhibit no blueshift and even redshift onthe (20-2-1)-plane, which possibly indicates reduced density oflocalized energy states and improved homogeneity. In the green (˜520 nm)spectral range (20-21) exhibits a strong blue-shift, whereas (20-2-1)demonstrates a redshift which again indicates better material quality.Such improved material quality in terms of reduction of localizedstates, increased homogeneity, or other could lead to improved gainproperties in the laser diode.

As an example, In InGaN-based diode lasers, inhomogeneousbroadening—induced by disorder in the InGaN active region (AR)—is a keyfactor in determining performance. Large broadening damps the lasergain, and therefore implies higher threshold current density for similarlaser cavity losses. This is especially critical for longer wavelengthemission (1>450 nm), where the large fraction of In in the AR tends tomake inhomogeneous broadening more problematic. Therefore, it isdesirable to identify means to reduce inhomogeneous broadening, andmethods to characterize it.

In a specific embodiment, the present method and devices uses absorptionspectra to characterize inhomogeneous broadening. The two metricsinclude: (i) the slope of the absorption near the band-edge (a sharperabsorption is related to more homogeneous material), and (ii) the Stokesshift between the band gap of absorption spectra and thephotoluminescence peak wavelength (a large Stokes shift is typicallyrelated to localized states, which are more prevalent in disorderedmaterials). In the following descriptions, we illustrated the differentbehavior of inhomogeneous broadening in m-plane, (20-21), and (20-2-1)samples grown under typical conditions.

FIGS. 5 through 7 illustrate band edge adsorption data according toembodiments of the present invention. FIG. 5 illustrates an example ofan absorption spectra of m-plane and (20-2-1) samples. The circle regionis the absorption spectra, which is near the onset of absorption. Theabsorption spectra are, to first order, quadratic near the onset ofabsorption (circled region), and therefore can be characterized by aconstant number such as the second derivative, which is referred to asthe slope. The bandgap energy E_(gap) is estimated from the onset of theabsorption spectra (arrow). The second derivative of the absorptionspectra will be called “slope” in the FIG. 6. The band gap energy, E gapin the FIG. 6, is estimated from the onset of the absorption spectra,where the arrow is.

FIG. 6 illustrates the slope of the absorption spectra as the functionof bandgap energy (E gap) for the laser diodes grown on m-plane, (20-21)and (20-2-1). The lower slope value implies the inhomogeneous broadeningin the MQW and thus degraded laser performance. At similar wavelength(bandgap energy), samples grown on (20-21) and (20-2-1) have higherslope value than the samples grown on m-plane. A lower bandgap energyindicates longer wavelength and a higher bandgap energy indicates ashorter wavelength. The higher slope for the structures grown on (20-21)and (20-2-1) implies a more homogeneous active region InGaN materialthan that grown on m-plane. In the long wavelength side, samples grownon (20-2-1) have higher slope value than samples on (20-21). Thisindicates that the InGaN quantum wells on the samples grown on (20-2-1)are likely more homogeneous than samples grown on (20-21) in the longwavelength side (small Egap side).

FIG. 7 illustrates the Stokes shift of samples grown on m-plane, (20-21)and (20-2-1). m-plane samples show an increasing Stokes shift at longerwavelength, suggesting an increasing amount of localized states. (20-21)shows a linear relationship between gap wavelength and photoluminescencewavelength in the violet to blue region. (20-2-1) shows a linearrelationship between gap wavelength and photoluminescence wavelength allthe way out to 510 nm, indicating it may be a desirable choice for agreen laser diode.

FIG. 8 is a diagram of a laser device on a {20-2-1} plane, a {30-3-1}plane, or an offcut of these planes. As shown, the optical deviceincludes a gallium nitride substrate member 801. In a specificembodiment, the gallium nitride substrate member is a bulk GaN substratecharacterized by having a semipolar crystalline surface region, but canbe others. In a specific embodiment, the bulk nitride GaN substratecomprises nitrogen and has a surface dislocation density between about10E5 cm⁻² and about 10E8 cm⁻² or below 10E5 cm⁻². The nitride crystal orwafer may comprise Al_(x)In_(y)Ga_(1-x-y)N, where 0≤x, y, x+y≤1. In onespecific embodiment, the nitride crystal comprises GaN. In one or moreembodiments, the GaN substrate has threading dislocations, at aconcentration between about 10E5 cm⁻² and about 10E8 cm⁻², in adirection that is substantially orthogonal or oblique with respect tothe surface. As a consequence of the orthogonal or oblique orientationof the dislocations, the surface dislocation density is between about10E5 cm⁻² and about 10E7 cm⁻² or below about 10E5 cm⁻². In a specificembodiment, the device can be fabricated on a slightly off-cut semipolarsubstrate as described in U.S. Ser. No. 12/749,466 filed on Mar. 29,2010, which is incorporated by reference herein.

In a specific embodiment on the {20-2-1} GaN, the device has a laserstripe region formed overlying a portion of the off-cut crystallineorientation surface region. The laser stripe region is characterized bya cavity orientation substantially in a projection of a c-direction,which is substantially normal to an a-direction. The laser stripe regionhas a first end 807 and a second end 809 and is formed on a projectionof a c-direction on a {20-2-1} gallium and nitrogen containing substratehaving a pair of cleaved mirror structures which face each other. Thecleaved facets provide a reflective coating, no coating, anantireflective coating, or expose gallium and nitrogen containingmaterial.

In embodiments, the device has a first cleaved facet provided on thefirst end of the laser stripe region and a second cleaved facet providedon the second end of the laser stripe region. The first cleaved facet issubstantially parallel with the second cleaved facet. Mirror surfacesare formed on each of the cleaved surfaces. The mirror surface of thefirst cleaved facet is provided by a top-side skip-scribe scribing andbreaking process. The scribing process can use any suitable techniques,such as a diamond scribe or laser scribe. In a specific embodiment, thefirst mirror surface comprises a reflective coating. The reflectivecoating is selected from silicon dioxide, hafnia, and titania, tantalumpentoxide, zirconia, or combinations thereof. Depending upon theembodiment, the first mirror surface can also comprise ananti-reflective coating.

Also, in certain embodiments, the second cleaved facet comprises asecond mirror surface provided by a top side skip-scribe scribing andbreaking process. Preferably, the scribing is diamond scribed or laserscribed. In a specific embodiment, the second mirror surface comprises areflective coating, such as silicon dioxide, hafnia, and titania,tantalum pentoxide, zirconia, combinations, and the like.

In certain embodiments, the device has a first cleaved facet provided onthe first end of the laser stripe region and a second cleaved facetprovided on the second end of the laser stripe region. The first cleavedfacet is substantially parallel with the second cleaved facet. Mirrorsurfaces are formed on each of the cleaved surfaces. The mirror surfaceof the first cleaved facet is provided by a nicking and breaking processwhere a nick is induced in the semiconductor material using a laserscribe or diamond scribe. This nick behaves as a crack initiation sitesuch that during the breaking process a crack is induced and propagatesa cleavage place to form a cleaved facet. Guiding etches or scribes maybe used to guide the cleavage plane along a predetermined direction. Thenick scribing process can use any suitable techniques, such as a diamondscribe or laser scribe. In a specific embodiment, the first mirrorsurface comprises a reflective coating. The reflective coating isselected from silicon dioxide, hafnia, and titania, tantalum pentoxide,zirconia, or combinations thereof. Depending upon the embodiment, thefirst mirror surface can also comprise an anti-reflective coating.

Also, in certain embodiments, the second cleaved facet comprises asecond mirror surface provided by a nicking and breaking process where anick is induced in the semiconductor material using a laser scribe ordiamond scribe. The nick behaves as a crack initiation site such thatduring the breaking process a crack is induced and propagates a cleavageplace to form a cleaved facet. Guiding etches or scribes may be used toguide the cleavage plane along a predetermined direction. The nickscribing process can use any suitable techniques, such as a diamondscribe or laser scribe. In a specific embodiment, the second mirrorsurface comprises a reflective coating, such as silicon dioxide, hafnia,and titania, tantalum pentoxide, zirconia, combinations, and the like.

In certain embodiments, the device has a first etched facet provided onthe first end of the laser stripe region and a second etched facetprovided on the second end of the laser stripe region. The first etchedfacet is substantially parallel with the second etched facet. Mirrorsurfaces are formed on each of the etched surfaces. The mirror surfaceof the first etched facet is provided by a lithography and etchingprocess where the etching process is selected from one of the followingof chemical assisted ion beam etching (CAIBE), reactive ion etching(RIE), or inductively coupled plasma (ICP) etches. In a specificembodiment, the first mirror surface comprises a reflective coating. Thereflective coating is selected from silicon dioxide, hafnia, andtitania, tantalum pentoxide, zirconia, or combinations thereof.Depending upon the embodiment, the first mirror surface can alsocomprise an anti-reflective coating.

Also, in certain embodiments, the second etched facet comprises a secondmirror surface provided by a lithography and etching process alithography and etching process where the etching process is selectedfrom one of the following of chemical assisted ion beam etching (CAIBE),reactive ion etching (RIE), or inductively coupled plasma (ICP) etches.In a specific embodiment, the second mirror surface comprises areflective coating, such as silicon dioxide, hafnia, and titania,tantalum pentoxide, zirconia, combinations, and the like.

The laser stripe has a length from about 50 microns to about 3000microns, but is preferably between 400 microns and 1000 microns. Thestripe also has a width ranging from about 0.5 microns to about 50microns, but is preferably between 0.8 microns and 3 microns. In aspecific embodiment, the overall device has a width ranging from about0.5 microns to about 15.0 microns. In a specific embodiment, the widthis substantially constant in dimension, although there may be slightvariations. The width and length are often formed using a masking andetching process, which are commonly used in the art.

This invention provides an optical device structure capable of emitting501 nm and greater (e.g., 525 nm) light in a ridge laser embodiment. Thedevice preferably includes: (1) a gallium and nitrogen containingsubstrate configured with a {20-2-1} surface region, (2) an InGaNseparate confinement heterostructure, (3) a gallium nitrogen barrierlayer(s), (4) a plurality of InGaN quantum wells (2 to 7), (5) a galliumnitrogen barrier layer(s), (6) an AlGaN electron blocking layer, (7) ap-type gallium nitrogen cladding layer, and (8) a p+ gallium nitrogencontact layer.

FIG. 9 is a cross-sectional diagram of the laser device according to anembodiment of the present invention. FIG. 9 shows semipolar laser diode900 including, backside n-contact metal 901, Gan substrate 902, nGaNlayer 903, n-type separate confinement heterostructure 904, multiplequantum well region 905, guiding layer 906 such as an InGaN or GaNguiding layer, electron blocking layer 907, insulating layer 908, pGaNstripe 909, p-metal contact 910, and p-pad metal 911.

FIG. 10 is a simplified refractive index diagram of a laser structure.As shown, the laser structure includes a gallium and nitrogen containingsubstrate configured in a certain plane (20-2-1) orientation, an InGaNseparate confinement heterostructure, a plurality of InGaN quantumwells, and an AlGaN electron blocking layer. Barrier layers includingGaN are also included.

FIG. 11 is a refractive index diagram of a laser structure with anInGaN/GaN super lattice structure according to an alternative embodimentof the present invention. The superlattice structure is used in place ofor in addition to the SCH region to assist with optical modeconfinement. As shown, the superlattice structure includes a gallium andnitrogen containing substrate configured in a certain plane (20-2-1)orientation, an InGaN superlattice separate confinement heterostructure,a plurality of InGaN quantum wells, and an AlGaN electron blockinglayer. Barrier layers including GaN are also included.

In a specific embodiment, the present device and method includes variousindium content in the super-lattice, as noted below, and a number ofsuperlattice periods. Examples of variations according to the presentinvention can be found throughout the present specification and moreparticularly below.

-   -   1. Vary the In content in the superlattice from 3% to 12%        -   In_(0.03)Ga_(0.97)N (n=2.4456)        -   In_(0.06)Ga_(0.94)N (n=2.4788)        -   In_(0.09)Ga_(0.91)N (n=2.5146)        -   In_(0.12)Ga_(0.88)N (n=2.5542)    -   2. Vary the number of superlattice periods        -   20 periods        -   35 periods        -   50 periods        -   65 periods

FIGS. 12A and 12B illustrate confinement factors and estimated opticallosses associated with absorption in the p-cladding loss characteristicsof laser devices. FIG. 12A shows a plot of confinement factor (quantumwell overlap) against a number of superlattice periods for variousindium contents, e.g., 6%, 9%, 12%. As also shown, FIG. 12B shows a plotof p-cladding loss against a number of superlattice periods for thevarious indium contents, e.g., 6%, 9%, 12%. Also shown are thefollowing:

-   -   Compare to standard SCH (60 nm In_(0.06)Ga_(0.94)N):        -   Confinement factor=0.0203        -   PGaN Loss=8.20 cm⁻¹    -   Compare to HSSCH (30 nm In_(0.13)Ga_(0.87)N/10 nm GaN/30 nm        In_(0.13)Ga_(0.87)N):        -   Confinement factor=0.0297        -   PGaN Loss=6.49 cm⁻¹

As noted, we have demonstrated the superlattice structure, standard SCH,and HSSCH. In a specific embodiment, a ridge waveguide is fabricatedusing a certain deposition, masking, and etching processes. In aspecific embodiment, the mask is comprised of photoresist (PR) ordielectric or any combination of both and/or different types of them.The ridge mask is 1 micron to 2.5 microns wide for single lateral modeapplications or 2.5 μm to 30 μm wide for multimode applications. Theridge waveguide is etched by ion-coupled plasma (ICP), reactive ionetching (RIE), or other method. The etched surface is 5 nm to 250 nmabove the active region. A dielectric passivation layer is then blanketdeposited by any number of commonly used methods in the art, such assputter, e-beam, PECVD, or other methods. This passivation layer caninclude SiO₂, Si₃N₄, Ta₂O₅, or others. The thickness of this layer is 80nm to 400 nm thick. An ultrasonic process is used to remove the etchmask which is covered with the dielectric. This exposes the p-GaNcontact layer. P-contact metal is deposited by e-beam, sputter, or otherdeposition technique using a PR mask to define the 2D geometry. Thecontact layer can be Ni/Au but others can be Pt/Au or Pd/Au.

In certain embodiments, the present laser device (e.g., 510 nm to 550nm) achieves desirable wall plug efficiencies. That is, thewall-plug-efficiencies can be greater than 3%, greater than 5%, greaterthan 7% and greater than 10% at output powers of over 60 mW. In aspecific embodiment, the laser device (e.g., 430 nm to 480 nm) achievesdesirable wall plug efficiencies. That is, the wall-plug-efficienciescan be greater than 15%, greater than 20%, greater than 25% and greaterthan 30% at output powers of over 60 mW. In an alternative embodiment,the laser device (e.g., 430 nm to 480 nm) achieves desirable wall plugefficiencies. That is, the wall-plug-efficiencies can be greater than15%, greater than 20%, greater than 25% and greater than 30% at outputpowers of over 1.5 W.

It has been discovered that certain semipolar planes are moresusceptible to thermal degradation of the light emitting active regionduring the subsequent growth of the p-type layers above the activeregion such as electron blocking layers, p-cladding layers, andp-contact layers. This thermal degradation characteristic results inreduced brightness or optical output power from the light emittingregion using photoluminescence or electroluminescence measurements. Thereduced brightness indicates reduced internal efficiency of the materialdue to the introduction of defects that act as non-radiativerecombination centers. Such non-radiative recombination centersultimately reduce device efficiency and can even prevent laser diodeoperation.

To demonstrate this thermal degradation FIG. 13 presents a simplifiedplot illustrating the effects of growth temperature of the electronicblocking layers (EBL) and p-cladding layer(s) on the electroluminescence(EL) brightness for alternative nonpolar and semipolar planes foroptical devices. The laser device structures used blue emitting (440 nmto 455 nm) active regions with quantum well thicknesses of 50 Å to 60 Åon the several orientations of GaN. Light collection geometry was keptconstant for all measurements. Numbers by data points indicate growthtemperature in degrees Celsius of the EBL/p-cladding. As clearlyillustrated by this figure, certain semipolar planes such as (20-2-1)are very susceptible to active region degradation with the growth of thep-cladding layers. For (20-2-1) with an EBL/p-clad growth temperature of950° C./900° C., the EL brightness was reduced to less than 10% of thatof the same structure grown with an EBL/p-clad growth temperature of875° C./875° C. When the growth temperature of the EBL/p-clad wasincreased to 1000° C./1000° C. the EL brightness was even furtherreduced. The (20-21) oriented device shows an EL brightness reductionfrom 1.4 mW to 0.9 mW when the EBL/p-clad growth temperatures areincreased from 950° C./950° C. to 1000° C./1000° C. The alternate planesshown in FIG. 13 such as (30-31), (30-3-1), (50-5-2), and (10-10) do notshow such a drastic EL brightness reduction with increased growthtemperature of the EBL and the p-cladding layers.

In an embodiment for lasers or LEDs fabricated on a family of planesincluding, but not limited to, (30-3-2), (20-2-1), (30-3-1), (30-32),(20-21), (30-31) or any orientation within +/−10 degrees toward c-planeand/or a-plane from these orientations, the epitaxial device structurewould contain a thin, 5 nm to 20 nm, 20 nm to 100 nm, 100 nm to 300 nmp-type region grown above the light emitting or quantum well regions.This thin p-type layer or layers may be characterized by a p-typecladding layer, an electron blocking layer, some combination, or otherand could be comprised of GaN, AlGaN, InGaN, or InAlGaN and doped with ap-type species such as magnesium. Ultra-thin layers in this range grownat temperatures below, about equal to, or only slightly hotter (10° C.to 75° C.) than the growth temperature used for the light emittinglayers would mitigate the thermal degradation to the light emittinglayers that occurs when the layers are grown hotter or thicker. Thereduced thermal degradation is a result of the relatively short growthtime and the low growth temperature required for deposition of the thinp-clad layer. The benefit would perhaps be greater for a laser diodesince much thicker p-type cladding layers are required in a laser diodecompared to an LED, and therefore one would expect a larger degree ofthermal degradation to the active region during the growth of the p-cladin a laser structure.

After the epitaxial growth is completed by MOCVD or other method such asMBE, one or more conducting oxide layers such as indium-tin-oxide (ITO)or zinc oxide (ZnO) would then be deposited directly on or generallyabove the thin p-cladding layer. These conducting oxide layers can bedeposited at a temperature lower than a typical p-cladding growthtemperature and even substantially lower than the growth temperature ofthe light emission region. This will prevent or drastically reduce anythermal degradation to the light emission region that would haveoccurred during the epitaxial growth of the conventional p-claddingregion. The resulting conducting oxide layer can act as a p-claddingregion in both laser and LED structures and can enable the formation ofa good p-contact on top of the conducting oxide layer that results inohmic or quasi-ohmic characteristics. Additionally, the conducting oxidelayers can have optical absorption coefficients in the blue and greenwavelength ranges of interest that are lower or significantly lower thanthe optical absorption coefficient of a typical highly doped epitaxialp-type cladding regions such as GaN or AlGaN, and may therefore help toreduce optical absorption for lower internal losses in a laser cavity orhigher extraction efficiency in an LED device. In an alternativeembodiment, metallic layers such as silver may be used in place ofconducting oxide layers.

In another embodiment for lasers or LEDs fabricated on a family ofplanes including, but not limited to, (30-3-2), (20-2-1), (30-3-1),(30-32), (20-21), (30-31) or any orientation within +/−10 degrees towardc-plane and/or a-plane from these orientations, the epitaxial devicestructure would contain a p-type cladding region grown at very lowgrowth temperature while still enabling an acceptable voltagecharacteristic within the device. The p-cladding layer could becomprised of GaN, AlGaN, InGaN, or InAlGaN and could be doped with aspecies such as magnesium. The very low growth temperature would be lessthan, equal to, or only slightly higher (10° C. to 50° C.) than thegrowth temperature used for the light emitting layers. More typically,the p-cladding region is grown at temperatures more than 50° C., morethan 100° C., or more than 150° C. hotter than the light emittinglayers. The substantially lower growth temperature would mitigatedegradation to the light emitting layers that typically occurs when thelayers are grown hotter or thicker. In a laser diode structure, thegrowth conditions, layer thickness, and layer composition would bedesigned to enable a laser device operable below 7V, operable below 6V,or operable below 5V. In an LED structure, the growth conditions, layerthickness, and layer composition would be designed to enable an LEDdevice operable below 6V, operable below 5V, or operable below 4V, oroperable below 3.5V.

FIG. 14 presents pulsed light versus current of single mode blue laserdiodes fabricated on (20-2-1) substrates. As shown, the blue lasersexhibit threshold currents in the 50 to 90 mA range and generate over 60mW of optical output power.

FIG. 15 presents continuous wave light versus current of a high powermulti-mode blue laser diode fabricated on a (30-3-1) substrate. Asshown, the blue laser exhibits a threshold current of 220 mA range andgenerates nearly 800 mW of optical output power at 1 Å of electricalinput current.

FIG. 16 shows an example schematic cross-section diagram of a laserdiode with a conductive oxide layer that comprises a substantial portionof the p-type cladding region. In this embodiment the waveguide striperegion is comprised entirely of the conductive oxide such that it formsall of the lateral index contrast to provide the lateral waveguide. Asan example, the conductive oxide can be an indium tin oxide, or othersuitable material. FIG. 16 shows device 1600 including backsiden-contact metal 1601, GaN substrate 1602, n-cladding 1603 such as a nGaNor nAlGaN cladding, separate confinement heterostructure 1604,multi-quantum well region 1605, guiding layer 1606 such as an InGaN orGaN guiding layer, electron blocking layer 1607, p-cladding layer 1608such as a pGaN layer, insulating dielectric layer 1612, conductive oxide1610 such as indium tin oxide, and p-pad metal 1611.

FIG. 17 shows another example schematic of a cross-section diagram of alaser diode with a conductive oxide layer that comprises a substantialportion of the p-type cladding region. In this embodiment the waveguidestripe region is comprised of a combination of a conductive and anepitaxially deposited p-type material such as p-type GaN, AlGaN,InAlGaN, or other gallium and nitrogen containing materials. In thisembodiment the conductive oxide and the epitaxially formed p-typematerial provides the lateral index contrast to provide the lateralwaveguide. FIG. 17 shows device 1700 including backside n-contact metal1701, GaN substrate 1702, n-cladding 1703 such as a nGaN or nAlGaNcladding, separate confinement heterostructure 1704, multi-quantum wellregion 1705, guiding layer 1706 such as an InGaN or GaN guiding layer,electron blocking layer 1707, p-cladding layer 1708 such as a pGaNlayer, insulating dielectric layer 1712, conductive oxide 1710 such asindium tin oxide, and p-pad metal 1711.

FIG. 18 provides an example process flow for forming a laser diode witha conductive oxide layer that comprises a substantial portion of thep-type cladding region. In this example the epitaxially grown wafer issubjected to a photolithography process that would result in openings inthe photoresist where the desired lasers stripes will be positioned.Following the photolithography the conductive oxide layer is depositedon the patterned wafer. The deposition methods could include sputtering,electron cyclotron resonance (ECR) deposition, or various otherevaporation methods. The ECR deposition occurs at a rate of 1-3angstroms per second, provides an ohmic contact to the p-layer it isdeposited on, and provides a suitable sheet resistance for andabsorption coefficient for forming an electrically conductive and lowoptical loss cladding region. This is followed by a lift-off processwhere the conductive oxide on top of the photoresist is removed from thewafer to result in laser stripe regions defined by the remainingconductive oxide stripes. In this embodiment the conductive oxide striperegion forms all of the lateral index contrast to provide the lateralwaveguide.

FIG. 19 provides an alternative example process flow for forming a laserdiode with a conductive oxide layer that comprises a substantial portionof the p-type cladding region. In this example the epitaxially grownwafer is subjected to a blanket deposition of a conductive oxide layer.The deposition methods could include sputtering, electron cyclotronresonance (ECR) deposition, or various other evaporation methods.Following the deposition a photolithography process is used to definelaser stripe patterns in the photoresist where the desired lasersstripes will be positioned. Following the photolithography step andetching process is carried out to remove the conductive oxide layer inthe field without the photoresist. This etching process could be wet ordry. An example of a wet etch chemistry would include HCl or HCl andFeCl₃. In this embodiment the conductive oxide stripe region forms allof the lateral index contrast to provide the lateral waveguide.

In a preferred embodiment an electron cyclotron resonance (ECR)deposition method is used to form an indium tin oxide (ITO) layer as theelectrically conductive oxide. By using the ECR process to deposit ITO alow damage will be inflicted on the semiconductor surface to enable verygood contact resistance. The bulk resistivity of these ITO films can beless than about 10E-4 ohm·cm, less than about 4E-4 ohm·cm, or less thanabout 3E-4 ohm·cm. This resistivity is drastically higher than typicalp-type GaN or p-type AlGaN which can be 3 to 4 orders of magnitudehigher. The lower resistivity will result in a lower device seriesresistance and hence a lower operating voltage within the laser diodefor higher efficiency. Further, the index of refraction of the ITO willbe lower than that of GaN, AlGaN, or InAlGaN to provide betterwaveguiding for laser diodes operating in the blue and green wavelengthregimes. For example, in the 450 nm range the index of refraction forITO is about 2.05 and for GaN it is about 2.48 while in the 525 nm rangethe index of refraction for ITO is about 1.95 and for GaN it is about2.41. The lower refractive index of the ITO will provide higher indexcontrast with the InGaN based active region and hence can provide higheroverlap with the quantum wells for higher modal gain. In a specificexample, the conductive oxide is formed at a temperature less than 350°C. or at a temperature less than 200° C. Additionally, for both theconductive oxide and the low temp pGaN, the laser device is operable inthe 500 nm to 600 nm range.

In an alternative embodiment an electron cyclotron resonance (ECR)deposition method is used to form a zinc oxide (ZnO) layer as theelectrically conductive oxide. By using the ECR process to deposit ZnO alow damage will be inflicted on the semiconductor surface to enable verygood contact resistance. The ECR deposition occurs at a rate of 1 Å to 3Å per second, provides an ohmic contact to the p-layer it is depositedon, and provides a suitable sheet resistance for and absorptioncoefficient for forming an electrically conductive and low optical losscladding region.

In an alternative specific embodiment, the present invention alsoprovides a method and structure using a low temperature pGaN orp-cladding region. In a specific embodiment, the p-GaN is grown at atemperature lower than 150° C. of a temperature used to grown the activeregion for the same optical device. Such optical device is configured ona specific semipolar plane, which is more prone to degradation andtherefore growth of the p-cladding is desirable at even a coolertemperature than the growth temperature of the active region to preventthermal damage. In an example, the present method provides a pGaN growthtemperature of less than 75° C. above the active region growthtemperature and less than 50° C. above the active region growthtemperature.

In some embodiments, the structure may include an optical blocking layerto prevent radiation leakage into the substrate and improve the devicecharacteristics. Although AlInN is a preferred embodiment for opticalblocking layers, or OBL, there can be other variations, modifications,and alternatives. An example of such OBL configured with the presentinvention can be found in U.S. application Ser. No. 13/288,268 filed onNov. 3, 2011, which is incorporated by reference herein. In a specificembodiment, the optical blocking region can include low Ga contentInAlGaN as the optical blocker. In other embodiments, the low Ga contentAl_(1-x-y)In_(y)Ga_(x)N would possess an x of less than 10%, x of lessthan 20%, or x of less than 30%.

In a preferred embodiment, the contact regions can also be subjected toselected scribing of n-type material.

In a specific embodiment, the present invention provides an opticaldevice, e.g., laser, LED. The device includes a gallium and nitrogencontaining material having a semipolar surface configured on one ofeither a (30-3-1), (30-31), (20-2-1), or (30-3-2) orientation. In anexample, the semipolar surface has an offcut of the orientation. Thedevice also has an n-type region overlying the semipolar surface. Thedevice has a superlattice region overlying the semipolar surface, thesuperlattice being characterized by 20 to 150 periods of alternating GaNand InGaN layers, alternating AlGaN and InAlGaN layers, alternatingAlGaN and GaN layers, or alternating GaN and InAlAGaN layers, each ofthe alternating layers in the superlattice having a thickness rangingfrom 0.5 nm to 20 nm. The device has an active region comprising atleast one active layer region overlying the superlattice region. Theactive region comprises a quantum well region or a doublehetero-structure region. The device has a p-type region overlying theactive region. The active region configured to emit electromagneticradiation with a wavelength between 400 nm and 500 nm or between 500 nmand 660 nm. In an example, the offcut of the orientation is between +/−5degrees toward a c-plane and between +/−10 degrees toward an a-plane.

In an alternative embodiment, the present invention provides a laserdevice. The device includes a gallium and nitrogen containing materialhaving a semipolar surface configured on one of either a (30-3-1),(30-31), (20-2-1), or (30-3-2) orientation. The semipolar surface has anoffcut of the orientation. The device has an n-type cladding regionoverlying the semipolar surface, and an active region comprising atleast one active layer region overlying the n-type cladding region. Theactive region comprises a quantum well region or a doublehetero-structure region. The device also has a p-type cladding regionoverlying the active region. The device has a laser stripe region formedoverlying a portion of the semipolar surface. The laser stripe region ischaracterized by a cavity orientation substantially parallel to theprojection of a c-direction. The laser stripe region has a first end anda second end. A first facet is provided on the first end of the laserstripe region and a second facet provided on the second end of the laserstripe region. The laser diode is configured to emit an electromagneticradiation with a peak wavelength of between 400 nm and 500 nm or between500 nm and 560 nm. In an example, the offcut of the orientation isbetween +/−5 degrees toward a c-plane and between +/−10 degrees towardan a-plane. In an example, the active region contains a plurality ofquantum well regions comprising 1 to 7 quantum wells. Each of thequantum wells comprises substantially InGaN. The plurality of quantumwell regions ranges in thickness from 2 nm to 5 nm or 5 nm to 10 nm.Alternatively, the active region contains a double heterostructureregion, which ranges in thickness from 10 nm to about 25 nm.

In an alternative embodiment, the present invention provides a laserdevice. The device has a gallium and nitrogen containing material havinga semipolar surface configured on one of either a (30-3-1), (30-31),(20-2-1), (20-21) or (30-3-2) orientation. The device has an n-typecladding region overlying the semipolar surface and an active regioncomprising at least one active layer region overlying the n-typecladding region. The device has a low temperature conductive oxideoverlying the active region. The low temperature conductive oxide isformed overlying the active region at a lower process temperature than aprocess temperature used to form the active region. The device also hasa laser stripe region formed overlying a portion of the semipolarsurface. The laser diode is configured to emit an electromagneticradiation with a peak wavelength of between 400 nm and 500 nm or between500 nm and 560 nm. In an example, the conductive oxide is selected fromindium tin oxide (ITO) or zinc oxide (ZnO).

In an alternative embodiment, the present invention provides a methodfor fabricating a laser device. The method includes providing a galliumand nitrogen containing material having a semipolar surface configuredon one of either a (30-3-1), (30-31), (20-2-1), (20-21) or (30-3-2)orientation. The method includes forming an n-type cladding regionoverlying the semipolar surface and forming an active region comprisingat least one active layer region overlying the n-type cladding region.The method includes depositing a low temperature conductive oxideoverlying the active region. The low temperature conductive oxide isformed overlying the active region at a lower process temperature than aprocess temperature used to form the active region. The method alsoincludes forming a laser stripe region formed overlying a portion of thesemipolar surface. The conductive oxide is selected from indium tinoxide (ITO) or zinc oxide (ZnO), which is transparent and can be formedat a lower temperature. Further details of the present method can befound throughout the present specification and more particularly below.

In an embodiment for lasers or LEDs fabricated on a family of planesincluding, but not limited to, (30-3-2), (20-2-1), (30-3-1), (30-32),(20-21), (30-31) or any orientation within +/−10 degrees toward c-planeand/or a-plane from these orientations, the epitaxial device structurewould contain a thin, 5 nm to 20 nm or 20 nm to 100 nm, p-claddingregion grown above the light emitting or quantum regions. This thinp-cladding layer could be comprised of GaN, AlGaN, InGaN, or InAlGaN anddoped with a species such as magnesium. Ultra-thin layers in this rangegrown at temperatures equal to or only slightly hotter (10° C. to 75°C.) than the growth temperature used for the light emitting layers wouldmitigate degradation to the light emitting layers that typically occurswhen the layers are grown hotter or thicker. The reduced thermaldegradation is a result of the relatively short growth time and the lowgrowth temperature required for deposition of the thin p-clad layer. Thebenefit would perhaps be greater for a laser diode since much thickerp-type cladding layers are required to an LED, and therefore one wouldexpect a larger degree of thermal degradation to the active regionduring the growth of the p-clad in a laser structure.

After the epitaxial growth is complete by MOCVD or other method, one ormore conducting oxide layers such as indium-tin-oxide (ITO) or zincoxide (ZnO) would then be deposited directly on or generally above thethin p-cladding layer. These conducting oxide layers can be deposited ata lower temperature lower than a typical p-cladding growth temperatureand even substantially lower than the growth temperature of the lightemission region. This will prevent or substantially reduce any thermaldegradation to the light emission region that would have occurred duringthe epitaxial growth of the conventional p-cladding region. Theresulting conducting oxide layer can act as a p-cladding region in bothlaser and LED structures and can enable the formation of a goodp-contact on top of the conducting oxide layer that results in ohmic orquasi-ohmic characteristics, Additionally, the conducting oxide layerscan have optical absorption coefficients at the wavelength ranges ofinterest which are lower or significantly lower than the opticalabsorption coefficient of a typical highly doped epitaxial p-typecladding regions such as GaN or AlGaN, and may therefore help to reduceoptical absorption for lower internal losses in a laser cavity or higherextraction efficiency in an LED device. In an alternative embodiment,metallic layers such as silver may be used in place of conducting oxidelayers.

In a specific embodiment, the present invention provides a laser device.The device has a gallium and nitrogen containing material having asemipolar surface configured on one of either a (30-3-1), (30-31),(20-2-1), (20-21) or (30-3-2) orientation. The device has an n-typecladding region overlying the semipolar surface and an active regioncomprising at least one active layer region overlying the n-typecladding region. The device has a p-type cladding region overlying theactive region, the p-type cladding region being formed from a lowtemperature GaN, AlInGaN, or AlGaN material. The p-type cladding regionis formed at a vicinity of or lower process temperature than a processtemperature of forming the active region. The device has a laser striperegion formed overlying a portion of the semipolar surface. The laserstripe region is characterized by a cavity orientation substantiallyparallel to the projection of a c-direction. The laser stripe region hasa first end and a second end, and respective first facet and secondfacet. The laser diode is configured to emit an electromagneticradiation with a peak wavelength of between 400 nm and 500 nm or between500 nm and 560 nm. In an example, the p-type cladding region is formedfrom the low temperature material at a temperature less than 75 degreesCelsius greater than the temperature used to form the active region. Thep-type cladding region is formed from the low temperature material at atemperature less than 50 degrees Celsius greater than the temperatureused to form the active region. In example, the p-type cladding regionis formed at a temperature equal to or less than the temperature used toform the active region, and the p-type cladding region is formed with anaverage growth rate of less than 1.5 angstroms per second. Furtherdetails of the present device and related method can be found throughoutthe present specification and more particularly below.

In another embodiment for lasers or LEDs fabricated on a family ofplanes including, but not limited to, (30-3-2), (20-2-1), (30-3-1),(30-32), (20-21), (30-31) or any orientation within +/−10 degrees towardc-plane and/or a-plane from these orientations, the epitaxial devicestructure would contain a p-type cladding region grown at very lowgrowth temperature while still enabling an acceptable voltagecharacteristic within the device. The p-cladding layer could becomprised of GaN, AlGaN, InGaN, or InAlGaN and could be doped with aspecies such as magnesium. The very low growth temperature would rangethose temperatures less than, equal to, or only slightly hotter (10° C.to 75° C.) than the growth temperature used for the light emittinglayers. More typically, the p-cladding region is grown at temperaturesmore than 50° C., more than 100° C., or more than 150° C. hotter thanthe light emitting layers. The substantially lower growth temperaturewould mitigate degradation to the light emitting layers that typicallyoccurs when the layers are grown hotter or thicker. In a laser diodestructure, the growth conditions, layer thickness, and layer compositionwould be designed to enable a laser device operable below 7V, operablebelow 6V, or operable below 5V. In an LED structure, the growthconditions, layer thickness, and layer composition would be designed toenable an LED device operable below 6V, operable below 5V, or operablebelow 4V, or operable below 3.5V.

In an alternative specific embodiment, the present invention provides alaser device configured on an offcut. The device includes a gallium andnitrogen containing material having a semipolar surface configured onone of either a (30-3-1) orientation, (30-31) orientation, (20-2-1)orientation, (20-21) orientation, or (30-3-2) orientation. The semipolarsurface has an offcut of the orientation characterized by an offcuttoward an a-plane. The offcut is toward the a-plane is greater inmagnitude than 1 degree and less than about 10 degrees. The offcut canalso be toward the a-plane is characterized by the absolute magnitude ofangle between 3 and 6 degrees or the offcut of the orientation ischaracterized by an offcut toward a c-plane; the offcut toward thec-plane is between +/−5 degrees. The device also has an n-type claddingregion overlying the semipolar surface and an active region comprisingat least one active layer region overlying the n-type cladding region.

As used herein, the term GaN substrate is associated with GroupIII-nitride based materials including GaN, InGaN, AlGaN, or other GroupIII containing alloys or compositions that are used as startingmaterials. Such starting materials include polar GaN substrates (i.e.,substrate where the largest area surface is nominally an (h k l) planewherein h=k=0, and l is non-zero), non-polar GaN substrates (i.e.,substrate material where the largest area surface is oriented at anangle ranging from about 80-100 degrees from the polar orientationdescribed above toward an (h k l) plane wherein l=0, and at least one ofh and k is non-zero) or semi-polar GaN substrates (i.e., substratematerial where the largest area surface is oriented at an angle rangingfrom about +0.1 to 80 degrees or 110-179.9 degrees from the polarorientation described above toward an (h k l) plane wherein l=0, and atleast one of h and k is non-zero).

As shown, the present device can be enclosed in a suitable package. Suchpackage can include those such as in TO-38 and TO-56 headers. Othersuitable package designs and methods can also exist, such as TO-9 andeven non-standard packaging. The present device can be implemented in aco-packaging configuration such as those described in U.S. PublicationNo. 2010/0302464, which is incorporated by reference herein.

In other embodiments, the present laser device can be configured in avariety of applications. Such applications include laser displays,metrology, communications, health care and surgery, informationtechnology, and others. As an example, the present laser device can beprovided in a laser display such as those described in U.S. PublicationNo. 2010/0302464, which is incorporated by reference herein.

FIG. 20 is a simplified diagram of a DLP projection device according toan embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. As shown in FIG. 20, a projection apparatus includes,among other things, a light source, a condensing lens, a color wheel, ashaping lens, and a digital lighting processor (DLP) board, and aprojection lens. The DLP board, among other things, includes aprocessor, a memory, and a digital micromirror device (DMD).

FIG. 21 is a simplified diagram illustrating a 3-chip DLP projectionsystem according to an embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 20, the3-chip DLP projection system includes a light source, optics, andmultiple DMDs, and a color wheel system. As shown, each of the DMDs isassociated with a specific color.

According to another embodiment, the present invention provides aprojection apparatus. The apparatus includes a housing having anaperture. The apparatus includes an input interface for receiving one ormore frames of images. The apparatus includes a laser source. The lasersource includes a blue laser diode, a green laser diode, and a red laserdiode. The blue laser diode is fabricated on a nonpolar or semipolaroriented Ga-containing substrate and has a peak operation wavelength ofabout 430 to 480 nm. The green laser diode is fabricated on a nonpolaror semipolar oriented Ga-containing substrate and has a peak operationwavelength of about 490 nm to 540 nm. The red laser could be fabricatedfrom AlInGaP. The apparatus includes a digital light processing chip(DLP) comprising three digital mirror devices. Each of the digitalmirror devices includes a plurality of mirrors. Each of the mirrorscorresponds to one or more pixels of the one or more frames of images.The color beams are respectively projected onto the digital mirrordevices. The apparatus includes a power source electrically coupled tothe laser sources and the digital light processing chip. Many variationsof this embodiment could exist, such as an embodiment where the greenand blue laser diode share the same substrate or two or more of thedifferent color lasers could be housed in the same packaged. In thiscopackaging embodiment, the outputs from the blue, green, and red laserdiodes would be combined into a single beam.

As an example, the color wheel may include phosphor material thatmodifies the color of light emitted from the light source. In a specificembodiment, the color wheel includes multiple regions, each of theregions corresponding to a specific color (e.g., red, green, blue,etc.). In an exemplary embodiment, a projector includes a light sourcethat includes blue and red light sources. The color wheel includes aslot for the blue color light and a phosphor containing region forconverting blue light to green light. In operation, the blue lightsource (e.g., blue laser diode or blue LED) provides blue light throughthe slot and excites green light from the phosphor containing region;the red light source provides red light separately. The green light fromthe phosphor may be transmitted through the color wheel, or reflectedback from it. In either case the green light is collected by optics andredirected to the microdisplay. The blue light passed through the slotis also directed to the microdisplay. The blue light source may be alaser diode or LED fabricated on non-polar or semi-polar oriented GaN.Alternatively, a green laser diode may be used, instead of a blue laserdiode with phosphor, to emit green light. It is to be appreciated thatcan be other combinations of colored light sources and color wheelsthereof.

As another example, the color wheel may include multiple phosphormaterials. For example, the color wheel may include both green and redphosphors in combination with a blue light source. In a specificembodiment, the color wheel includes multiple regions, each of theregions corresponding to a specific color (e.g., red, green, blue,etc.). In an exemplary embodiment, a projector includes a light sourcethat includes a blue light source. The color wheel includes a slot forthe blue laser light and two phosphor containing regions for convertingblue light to green light, and blue light and to red light,respectively. In operation, the blue light source (e.g., blue laserdiode or blue LED) provides blue light through the slot and excitesgreen light and red light from the phosphor containing regions. Thegreen and red light from the phosphor may be transmitted through thecolor wheel, or reflected back from it. In either case the green and redlight is collected by optics and redirected to the microdisplay. Theblue light source may be a laser diode or LED fabricated on non-polar orsemi-polar oriented GaN. It is to be appreciated that can be othercombinations of colored light sources and color wheels thereof.

As another example, the color wheel may include blue, green, and redphosphor materials. For example, the color wheel may include blue, greenand red phosphors in combination with a ultra-violet (UV) light source.In a specific embodiment, color wheel includes multiple regions, each ofthe regions corresponding to a specific color (e.g., red, green, blue,etc.). In an exemplary embodiment, a projector includes a light sourcethat includes a UV light source. The color wheel includes three phosphorcontaining regions for converting UV light to blue light, UV light togreen light, and UV light and to red light, respectively. In operation,the color wheel emits blue, green, and red light from the phosphorcontaining regions in sequence. The blue, green and red light from thephosphor may be transmitted through the color wheel, or reflected backfrom it. In either case the blue, green, and red light is collected byoptics and redirected to the microdisplay. The UV light source may be alaser diode or LED fabricated on non-polar or semi-polar oriented GaN.It is to be appreciated that can be other combinations of colored lightsources and color wheels thereof.

According to yet another embodiment, the present invention provides aprojection apparatus. The apparatus includes a housing having anaperture. The apparatus includes an input interface for receiving one ormore frames of images. The apparatus includes a laser source. The lasersource includes a blue laser diode, a green laser diode, and a red laserdiode. The blue laser diode is fabricated on a nonpolar or semipolaroriented Ga-containing substrate and has a peak operation wavelength ofabout 430 to 480 nm. The green laser diode is fabricated on a nonpolaror semipolar oriented Ga-containing substrate and has a peak operationwavelength of about 490 nm to 540 nm. The red laser could be fabricatedfrom AlInGaP. The green laser diode has a wavelength of about 490 nm to540 nm. The laser source is configured produce a laser beam by comingoutputs from the blue, green, and red laser diodes. The apparatusincludes a digital light processing chip comprising three digital mirrordevices. Each of the digital mirror devices includes a plurality ofmirrors. Each of the mirrors corresponds to one or more pixels of theone or more frames of images. The color beams are respectively projectedonto the digital mirror devices. The apparatus includes a power sourceelectrically coupled to the laser sources and the digital lightprocessing chip. Many variations of this embodiment could exist, such asan embodiment where the green and blue laser diode share the samesubstrate or two or more of the different color lasers could housed inthe same packaged. In this copackaging embodiment, the outputs from theblue, green, and red laser diodes would be combined into a single beam.

As an example, the color wheel may include phosphor material thatmodifies the color of light emitted from the light source. In a specificembodiment, the color wheel includes multiple regions, each of theregions corresponding to a specific color (e.g., red, green, blue,etc.). In an exemplary embodiment, a projector includes a light sourcethat includes blue and red light sources. The color wheel includes aslot for the blue color light and a phosphor containing region forconverting blue light to green light. In operation, the blue lightsource (e.g., blue laser diode or blue LED) provides blue light throughthe slot and excites green light from the phosphor containing region;the red light source provides red light separately. The green light fromthe phosphor may be transmitted through the color wheel, or reflectedback from it. In either case the green light is collected by optics andredirected to the microdisplay. The blue light passed through the slotis also directed to the microdisplay. The blue light source may be alaser diode or LED fabricated on non-polar or semi-polar oriented GaN.Alternatively, a green laser diode may be used, instead of a blue laserdiode with phosphor, to emit green light. It is to be appreciated thatcan be other combinations of colored light sources and color wheelsthereof.

As another example, the color wheel may include multiple phosphormaterials. For example, the color wheel may include both green and redphosphors in combination with a blue light source. In a specificembodiment, the color wheel includes multiple regions, each of theregions corresponding to a specific color (e.g., red, green, blue,etc.). In an exemplary embodiment, a projector includes a light sourcethat includes a blue light source. The color wheel includes a slot forthe blue laser light and two phosphor containing regions for convertingblue light to green light, and blue light and to red light,respectively. In operation, the blue light source (e.g., blue laserdiode or blue LED) provides blue light through the slot and excitesgreen light and red light from the phosphor containing regions. Thegreen and red light from the phosphor may be transmitted through thecolor wheel, or reflected back from it. In either case the green and redlight is collected by optics and redirected to the microdisplay. Theblue light source may be a laser diode or LED fabricated on non-polar orsemi-polar oriented GaN. It is to be appreciated that can be othercombinations of colored light sources and color wheels thereof.

As another example, the color wheel may include blue, green, and redphosphor materials. For example, the color wheel may include blue, greenand red phosphors in combination with a ultra-violet (UV) light source.In a specific embodiment, color wheel includes multiple regions, each ofthe regions corresponding to a specific color (e.g., red, green, blue,etc.). In an exemplary embodiment, a projector includes a light sourcethat includes a UV light source. The color wheel includes three phosphorcontaining regions for converting UV light to blue light, UV light togreen light, and UV light and to red light, respectively. In operation,the color wheel emits blue, green, and red light from the phosphorcontaining regions in sequence. The blue, green and red light from thephosphor may be transmitted through the color wheel, or reflected backfrom it. In either case the blue, green, and red light is collected byoptics and redirected to the microdisplay. The UV light source may be alaser diode or LED fabricated on non-polar or semi-polar oriented GaN.It is to be appreciated that can be other combinations of colored lightsources and color wheels thereof.

In one or more other embodiments, the present invention may includeaspects of those described in U.S. Publication No. 2011/0064101; U.S.application Ser. No. 13/288,268 filed on Nov. 3, 2011; and U.S.application Ser. No. 13/357,518, each of which is incorporated byreference herein.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. As used herein, the term “substrate” can mean the bulk substrateor can include overlying growth structures such as a gallium andnitrogen containing epitaxial region, or functional regions such asn-type GaN, combinations, and the like. Therefore, the above descriptionand illustrations should not be taken as limiting the scope of thepresent invention which is defined by the appended claims.

What is claimed is:
 1. A system comprising: a housing having anaperture; an input interface for receiving one or more frames of images;a laser diode device; a power source electrically coupled to the laserdiode device; wherein the laser diode device is configured to emitelectromagnetic radiation with a peak wavelength of between 400 nm and500 nm or between 500 nm and 560 nm; and an application configured withthe laser diode device, the laser diode device comprising: a gallium andnitrogen containing material comprising a semipolar surface configuredon a (30-3-1) orientation, a (30-31) orientation, a (20-2-1)orientation, or a (30-3-2) orientation, the semipolar surface having anoffcut of the orientation; an n-type cladding region overlying thesemipolar surface; an active region comprising at least one lightemitting active layer region overlying the n-type cladding region; thelight emitting active layer region comprising a quantum well region or adouble hetero-structure region; a p-type cladding region overlying theactive region; a conductive oxide overlying the p-type cladding region;a laser stripe region comprising at least a portion of the p-typecladding region and the conductive oxide, the laser stripe region beingcharacterized by a cavity orientation substantially parallel to theprojection of a c-direction, the laser stripe region having a first endand a second end; a first facet provided on the first end of the laserstripe region; and a second facet provided on the second end of thelaser stripe region.
 2. The system of claim 1, wherein the offcut of theorientation is between +/−5 degrees toward a c-plane and between +/−10degrees toward an a-plane; and wherein the active region contains aplurality of quantum well regions comprising 1 to 7 quantum wells, eachof the quantum well regions comprising substantially InGaN; theplurality of quantum well regions ranging in thickness from 2 nm to 5 nmor from 5 nm to 10 nm; or wherein the active region contains a doubleheterostructure region; the double heterostructure region ranging inthickness from 10 nm to about 25 nm.
 3. The system of claim 1, whereinthe first facet and the second facet are etched facets formed using alithography and etching process.
 4. The system of claim 1, wherein theapplication is selected from one of a laser display application, ametrology application, a communications application, a health careapplication, a surgery application, and an information technologyapplication.
 5. A system comprising: a housing having an aperture; aninput interface for receiving one or more frames of images; a greenlaser device; a power source electrically coupled to the green laserdevice; wherein the green laser device is configured to emitelectromagnetic radiation with a peak wavelength of between 500 nm and580 nm; and an application configured with the green laser device, thegreen laser device comprising: a gallium and nitrogen containingmaterial comprising a semipolar surface configured on a (30-3-1)orientation, a (30-31) orientation, a (20-2-1) orientation, a (20-21)orientation, or a (30-3-2) orientation, the semipolar surface having anoffcut of the orientation; an n-type cladding region overlying thesemipolar surface; an active region comprising at least one lightemitting active layer region overlying the n-type cladding region; thelight emitting active layer region comprising a quantum well region or adouble hetero-structure region; a laser stripe region overlying theactive region, the laser stripe region comprising conductive oxide andbeing characterized by a cavity orientation substantially parallel tothe projection of a c-direction, the laser stripe region having a firstend and a second end; a first facet provided on the first end of thelaser stripe region; and a second facet provided on the second end ofthe laser stripe region.
 6. The system of claim 5, wherein the offcut ofthe orientation is between +/−5 degrees toward a c-plane and between+/−10 degrees toward an a-plane; wherein the active region contains aplurality of quantum well regions comprising 1 to 7 quantum wells, eachof the quantum well regions comprising substantially InGaN; theplurality of quantum well regions ranging in thickness from 2 nm to 5 nmor from 5 nm to 10 nm; or wherein the active region contains a doubleheterostructure region; the double heterostructure region ranging inthickness from about 10 nm to about 25 nm; and wherein the first facetand the second facet are formed using a lithography and etching process.7. The system of claim 5, wherein the conductive oxide comprises atleast one of indium tin oxide (ITO) or zinc oxide (ZnO).
 8. The systemof claim 5, comprising a p-type gallium and nitrogen containing layeroverlying the active region and underlying the conductive oxide.
 9. Thesystem of claim 5, wherein the first facet and the second facet areetched facets formed using a lithography and etching process.
 10. Thesystem of claim 5, wherein the application is selected from one of alaser display application, a metrology application, a communicationsapplication, a health care application, a surgery application, and aninformation technology application.
 11. A system comprising: a housinghaving an aperture; an input interface for receiving one or more framesof images; a laser device; a power source electrically coupled to thelaser device; wherein the laser device is configured to emit anelectromagnetic radiation with a peak wavelength of between 400 nm and500 nm or between 500 nm and 580 nm; and an application configured withthe laser device, the laser device comprising: a gallium and nitrogencontaining material comprising a semipolar surface configured on a(30-31) orientation, a (30-31) orientation, a (20-2-1) orientation, a(20-21) orientation, or a (30-3-2) orientation, the semipolar surfacehaving an offcut of the orientation, the offcut of the orientationcharacterized by an offcut toward an a-plane; the offcut toward thea-plane being greater in magnitude than 1 degree and less than about 12degrees; an n-type cladding region overlying the semipolar surface; anactive region comprising at least one light emitting active layer regionoverlying the n-type cladding region; the light emitting active layerregion comprising a quantum well region or a double hetero-structureregion; a p-type cladding region overlying the active region; a laserstripe region overlying a portion of the semipolar surface, the laserstripe region being characterized by a cavity orientation substantiallyparallel to the projection of a c-direction, the laser stripe regionhaving a first end and a second end; a first etched facet provided onthe first end of the laser stripe region; and a second etched facetprovided on the second end of the laser stripe region.
 12. The system ofclaim 11, wherein the offcut toward the a-plane is characterized by anabsolute magnitude of angle between 3 and 10 degrees.
 13. The system ofclaim 11, wherein the offcut of the orientation is characterized by anoffcut toward a c-plan of between +/−5 degrees.
 14. The system of claim11, wherein the application is selected from one of a laser displayapplication, a metrology application, a communications application, ahealth care application, a surgery application, and an informationtechnology application.